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ENERGY EFFICIENCY MARCH 2017 • E&MJ 49 www.e-mj.com Navigating the Energy Curve Comminution is by far the largest consumer of energy in a typical mining operation, amounting to as much as 35% of a site's en- tire energy usage — roughly five times the energy consumed by the flotation/concentration stage of processing. However, gains in flotation energy efficiency and overall recovery performance can also have a beneficial effect on comminution energy costs. For example, if a flotation circuit can be modified or adjusted to efficiently handle coarser particles, the energy cost of grinding ore down to an unneeded fineness often can also be reduced. But how does a mine know where it stands relative to industry norms when it comes to comminution-related energy consump- tion? Check out the Coalition for Energy Efficient Comminution's (CEEC) Energy Curve Program, a tool which allows comminu- tion circuit operators to benchmark the energy efficiency of their operations and to contribute anonymously to the database on which the tool is based. CEEC is a not-for-profit organization that aims to accelerate implementation of ecoefficient comminution and energy practices in the global mining industry. The comminution energy intensity of the mine is presented in a graphical form similar to a cost curve. Each mine is dis- played as a separate bar in a bar chart, the width of which rep- resents the annual production. The comminution energy intensi- ty is represented by the height of the bar. This allows individual mines to be ranked with respect to energy consumption, and displays the potential energy and cost bene fi ts of moving down the graph into more ef fi cient operating regimes. Anonymity of mine-specific data is maintained and the variability is visualized by constructing an "energy curve." CEEC believes that since these types of curves are well-known in the mining industry, this familiar format can be used to motivate behaviors that will move the mine down the curve. This approach also allows flexibility in the way comminution energy intensity is displayed (e.g., energy per rock milled or metal produced), thus providing a fairer com- parison between sites. According to CEEC, the practical applications of energy curves are numerous. They can be used to map the position of the mine as production progresses with year-on-year analy- sis. Operational efficiency improvements can be mapped on the curves to visually assess the magnitude of energy reductions achieved through various strategies. The efficiency with which the various comminution devices achieve size reduction can be mapped down a circuit to identify opportunities for improvement and the magnitude of achievable gains. CEEC announced in late 2016 that the Energy Curves da- tabase had grown to include more than 30% of global gold production, and also now contains 58% of global copper pro- duction, as well as other mined commodities. The energy curve program is supported by contributions from its sponsors and is offered free to the industry. would indicate a requirement of 18-24 minutes in conventional cells," he noted. "Of course, the scale-up to larger sized StackCells may also require a residence time multiplier like conventional cells, but similar results have been observed for other sulfides in StackCell units up to 1.2 m in diameter. In addition to the in- creased kinetics, the StackCell also pro- duces a higher grade in general because of the ability to wash the froth, which is only efficient because of the quiescent environment of the froth recovery stage. Similar results were also observed for the molybdenum contained in this stream." Eriez pointed out that a dramatic re- duction in the amount of time to recover the material has a major impact on the working volume of the cells, capital cost, plant space and energy consumption. The major improvement in energy con- sumption is achieved by concentrating the energy required for bubble-particle at- tachment in a small volume and then not adding excessive energy to maintain parti- cles in suspension in the tank, which can be disadvantageous to the froth recovery zone. The StackCell is now being actively tested in a number of metal ore systems with traditionally slow-floating minerals. In conclusion, Wasmund told E&MJ that, combined with the HydroFloat for coarse flotation, the StackCell for slow-floating midsize range particles has the ability to revolutionize mineral pro- cessing by reducing energy consumption, as well as capital costs — just two ex- amples of how the company is working to change the mineral processing business to be less energy and capital intensive for the future. References * P. Mehrfert, "Investigating the Potential of HydroFloat Coarse Particle Flotation," Canadian Mineral Processors National Conference, Ottawa, 2017. **L. Christodoulou, "Alternative Ap- proach to Base and Precious Metals Flow Sheet Design," Colorado MPD, 2016. Recovery kinetics for a three-stage StackCell train, benchmarked against the Denver lab cell kinetic response for the same feed.